To observe a microscopic image of an object, a microscope such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM) is used. In general, these microscopes have a housing which accommodates a sample evacuated to capture an image of the sample under a vacuum state. However, the vacuum state may damage a sample such as a biochemical sample or a liquid sample, or change a state of the sample. On the contrary, there are large needs for observing such samples using an electron microscope, and in recent years, a device such as an SEM and a sample holder that enables the observation of a target sample at one air pressure has been developed.
In principle, these devices have an electron-beam-transmittable diaphragm between an electron optical system and the sample to partition the housing into a vacuum space and an atmospheric space. Therefore, these devices have a common configuration which has the diaphragm between the electron optical system and the sample.
For example, Patent Literature 1 discloses an SEM that includes an electronic optical lens column provided with an electron source thereof arranged at a lower side and an objective lens arranged at an upper side, and a diaphragm which is able to transmit an electron beam via an O-ring on an electron-beam-emitting aperture at an end of the electronic optical lens column. The invention described in the Patent Literature 1 places the liquid containing an observed sample directly on the diaphragm, irradiates a primary electron beam on the lower surface of the sample, and detects reflected electrons or secondary electrons to perform the SEM observation. The sample is held in a space defined by the diaphragm and an annular member disposed around the diaphragm, and further this space is filled with a liquid such as water.